feat(devcontainer): add devcontainer.json

Builds from CI builder base, runs as non-root dev user.
postCreateCommand bootstraps PVC home dir on first session.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.devcontainer/devcontainer.json

@@ -0,0 +1,18 @@
+{
+  "name": "foxhunt",
+  "build": {
+    "dockerfile": "Dockerfile",
+    "context": "..",
+    "args": {
+      "CI_BUILDER_IMAGE": "rg.fr-par.scw.cloud/foxhunt-ci/ci-builder:latest"
+    }
+  },
+  "remoteUser": "dev",
+  "containerEnv": {
+    "SQLX_OFFLINE": "true",
+    "CUDA_COMPUTE_CAP": "90",
+    "EDITOR": "vim"
+  },
+  "postCreateCommand": "/usr/local/bin/init-home.sh",
+  "postStartCommand": "claude --version && cargo --version && kubectl cluster-info 2>/dev/null || true"
+}